1. "bye" You can say "수고" instead of "bye" if your friend is doing something at that time. 2. "Keep up the good work" You can say "수고하세요" if you want someone to keep his/her work going well. This is also used as a greeting. --> It's a kind of cultural difference in greetings. 3. 시험보느라 수고하셨어요. I appreciate you having a hard time to take the test.

thats right

Exactly :)